Stepping device



July 28, 1964 L. MILLER, JR

smpmc DEVICE Filed April 4, 1961 FICI 2 Sheets-Sheet 1 FIE-3 4 MENTOR Lzs TER Mum JA'.

ATTORNEYS y 28, 1954 L. MILLER, JR I 3,142,188

STEPPING nsvxcs Filed April 4. 1961 2 Sheets-Sheet 2 FIGS INVENT OR Les r51? MILLER JR.

I M WW ATTORNEYS United States Patent 3,142,188 STEPPING DEVHCE Lester Miller, Jr., Danhury, Conn, assignor to American Machine & Foundry Company, a corporation of New Jersey Fiied Apr. 4, 1961, Ser. No. 1tl0,716 13 Claims. (Cl. 74142) This invention relates to stepping devices and more particularly to improvements in stepping devices of the type disclosed in copending application Serial No.89,247, filed February 14, 1961, by Siegfried Godel.

Stepping devices of the type disclosed in the abovementioned copending application comprise a ratchet wheel which is driven, in opposite directions, through successive angular positions by a pair of driving pawls. The driving pawls are actuated by a pair of electromagnets. Since such stepping devices can be operated at relatively high speeds, the time during which the ratchet wheel is moved between adjacent positions is relatively short. Consequently, the various movable parts are moved at extremely high speeds and develop considerable inertia.

A problem frequently exists in such devices because the high inertia of the moving parts not only tends to cause some of the parts to jam or wedge together but it also tends to cause the ratchet wheel to overshoot its position. This problem is often aggravated because normal wear between coacting parts increases the tendency for jamming and overshooting to occur. Accordingly, one of the objects of this invention is to provide a stepping device which can be successfully operated at both high and low speeds without jamming and without overshooting.

Another object is to provide an improved stepping device having pawl means arranged to limit movement of the ratchet wheel so that rotation of the ratchet wheel occurs in steps of equal increments.

Still another object is to provide a stepping device hav ing means engageable with the ratchet wheel to absorb the momentum of the ratchet wheel and limit angular displacement thereof.

Another object is to provide a stepping device having stop pawls for limiting rotation of a ratchet wheel, the stop pawls being arranged to minimize wear due to the coaction between the ratchet wheel and the stop pawls.

A further object is to devise an improved bidirectional stepping motor.

In order that the manner in which these and other objects are attained in accordance with the invention can be understood in detail, reference is had to the accompanying drawings, which form a part of this specification, and wherein:

FIG. 1 is a front elevational view of a stepping device embodying the invention;

FIGS. 2-4 are views similar to FIG. 1 with the electromagnets removed, illustrating various operating positions of portions of the device;

FIG. 5 is a front elevational view illustrating how the detent pawls are coupled to their associated stop pawls;

FIG. 6 is a plan view illustrating how the driving pawls are mounted upon their associated armatures;

FIG. 7 is a horizontal sectional view taken along line 7-7 of FIG. 2; and

FIG. 8 is a view illustrating the tooth profile of the ratchet wheel employed in the device of FIG. 1.

Referring now to the drawings in detail, the embodiment of the invention. there shown includes a ratchet wheel 10, a pair of driving pawls 11 and 12, a pair of detent pawls 13 and 14, a pair of stop pawls 15 and 16, a pair of armatures 17 and 18 and a pair of electromagnets 19 and 20 mounted in substantial bilateral symmetry on a support bracket 21.

Support bracket 21 includes a flat horizontal base 22, a flat upright portion 23 which extends upwardly from the rear of base 22, a pair of lugs 24 located one on each side of base 22 in front of portion 23, and an arm or support 25 struck out of base 22 and extending upwardly in front of portion 23, lugs 24 being closer to the front of base 22 than support 25. An inverted U-shaped bracket 26 has its ends secured to lugs 24 by suitable means such as a pair of screws.

The upper ends of electromagnets 19 and 20 are secured to the cross bar of bracket 26 so that the electromagnets extend downwardly from the cross bar in parallel relation toward base 22. Electromagnets 19 and 20 are of conventional construction and include a pair of downwardly facing poles 27 and 28 spaced above base 22. The electromagnets are selectively energizable, i.e., only one electromagnet at a time can be energized.

Ratchet wheel 14) is suitably mounted on support bracket 21 for rotation about an axis which extends perpendicular to and intersects the upper portion of upright portion 23. A stop member 29 is secured to upright portion 23 adjacent to ratchet wheel 19 and includes a fiat body portion 30 which abuts the front face of upright portion 23. A pair of stops 31 and 32 and a pair of guides 33 and 34 extend forwardly of flat body portion 30, guide 33 being adjacent to but spaced below stop 31 and guide 34 being adjacent to but spaced below stop 32.

Pawls 13, 14, 15 and 16 and armatures 17 and 18 are rotatably mounted on a pivot pin 35 which is supported by and extends between support 25 and the lower end of upright portion 23. Pin 35 is supported above base 22 so that the axis of pivot pin 35 is parallel to the axis of rotation of ratchet wheel 10.

As shown in FIG. 7, pivot pin 35 includes an enlarged slotted head 36 which abuts the front face of support 25. The rear end of pin 35 extends through upright portion 23 and is threaded for receiving a nut 37 to secure the pivot pin in place. A pair of washers 38 and 39 are mounted on the pivot pin and abut support 25 and upright portion 23, respectively. Armature 17 is mounted in engagement with the rear face of washer 38 and includes a hub 40 which extends rearwardly along pivot pin 35. Armature 18 is mounted in engagement with the front face of washer 39 and includes a hub 41 which extends forwardly along pivot pin 35, the front face of hub 41 abutting the rear face of hub 40. Detent pawl 14 and stop pawl 15 are supported on hub 40 for rotation about the axis of pivot pin 35. Similarly, detent pawl 13 and stop pawl 16 are supported by hub 41 for rotation about the axis of the pivot pin. Since the pivot pin is parallel to the ratchet wheel, it is obvious, then, that pawls 13, 14, 15 and 16 and armatures 17 and 18 are mounted for rotation about an axis parallel to the axis of rotation of ratchet wheel 10.

Armature 13 includes a flat body portion 42 which lies in a plane perpendicular to the axes of pivot pin 35 and of ratchet wheel 10. A strengthening rib 43 encircles a portion of the periphery of body 42. Armature 18 also includes a portion 44 which extends forwardly from the lower edge of body 42 and lies beneath pole 28 and above face 22. At least portion 44 is of magnetic material so that energization of electromagnet 20 is effective to attract portion 44 toward pole 28 and thereby rotate armature 18 in a counterclockwise direction from its unactuated position, illustrated in FIG. 1, to its actuated position, illustrated in FIG. 4.

Body 42 of armature 18 is irregularly shaped and includes a leg which extends upwardly along the right side of ratchet wheel 14) and operatively supports driving pawl 12 to the right of the ratchet wheel. As best seen in FIG. 6, armature 18 includes a pair of spaced cars 45 which embrace the sides of driving pawl 12. A pivot pin 46 extends through ears 45 and driving pawl 12 and supports driving pawl 12 for rotation relative to armature 18. Driving pawl 12 is thus supported for rotation about an axis parallel to the axis of rotation of ratchet wheel 11 and to the axis of pivot pin 35. Driving pawl 12 extends from the pivot pin toward ratchet wheel 16 and in the space between stop 32 and guide 34. A pair of torsion springs 47 are mounted on pivot pin 46 and bias driving pawl 12 in a counterclockwise direction about pin 46 toward engagement with guide 34. Driving pawl 12 is effective, upon actuation of armature 18, to rotate ratchet wheel in a counterclockwise direction, in a manner more fully described hereinafter.

Similarly, armature 17 has a portion 48 which lies between base 22 and pole 27. Portion 48 is of magnetic material so that, when electromagnet 19 is energized, electromagnet 19 attracts portion 48 toward pole 27 and rotates armature 17 in a clockwise direction. Armature 17 supports driving pawl 11 in a manner similar to that by which driving pawl 12 is supported on armature 18 so that driving pawl 11 is effective to rotate ratchet wheel 10 in a clockwise direction upon actuation of armature 17 and electromagnet 19.

Armature 17 includes an upright arm 49 which extends upwardly on the right side of the longitudinal center of the stepping device. Arm 49 is provided with a straight edge 51) which is engageable with a straight edge 51 of detent pawl 14. Edges 56 and 51 are normally engaged and form a coupling between armature 17 and detent 14 so that, when the armature is moved from its unactuated to its actuated position, edge 50 bears against edge 51 and rotates detent pawl 14 in a clockwise direction away from engagement with ratchet wheel 19 and, when electromagnet 19 is deenergiz ed, detent pawl 14 imparts a torque to armature 17 which rotates armature 17 from its actuated position to its unactuated position.

In a similar manner, armature is coupled to detent pawl 13 so that, when the armature is moved from its unactuated position to its actuated position, armature 18 rotates detent pawl 13 in a counterclockwise direction and so that detent pawl 13 will rotate armature 18 toward its unactuated position, in a manner more fully described hereinafter.

As best seen in FIG. 5, pawl 14 has a second straight edge 53 which abuts a straight edge 54 of stop pawl 15 to provide a coupling so that stop pawl 15 is actuated into operative engagement with ratchet wheel 11), in a manner described hereafter, in response to movement of detent pawl 14. A helical tension spring 56 is connected at its ends to detent pawls 13 and 14 and biases these pawls toward each other and toward engagement with the lower left and the lower right quadrants of ratchet wheel 10, respectively. In a manner similar to that by which detent pawl 14 is coupled to armature 17 and stop pawl 15, detent pawl 13 is coupled to both armature 18 and stop pawl 16. A helical tension spring 55 biases stop pawls 15 and 16 toward each other and toward engagement with the lower left and the lower right quadrants, respectively, of ratchet wheel 10. Since the stop pawls are normally disengaged, spring 56 is stronger than spring 55 to allow normal engagement of the detent pawls.

Ratchet wheel 10 is provided with a plurality of major teeth 57 and minor teeth 58 spaced about the periphery thereof, there being one minor tooth between each pair of adjacent major teeth. Each tooth projects radially outwardly from ratchet wheel 11 and has flat side surfaces lying in plates which intersect at an apex such that a radial line passing through the apex bisects the angle between the side surfaces. The planes at which the side surfaces of each tooth lie are parallel to the axis of rotation of the ratchet wheel.

The radial distance to the apex of each minor tooth 58 is less than the radial distance to a cord extending between the apexes of the adjacent major teeth. As best seen in FIG. 8, each of the side surfaces of each minor tooth lies in a plane which passes through the apex of the major tooth adjacent the other side of the minor tooth. Thus, side 5% of minor tooth 58a lies in a plane which passes through the apex of major tooth 57b, and side surface 69 of minor tooth 53a lies in a plane which passes through the apex of major tooth 5711.

Since the free end of pawls 13, 14, 15 and 16, which engage ratchet wheel 10, are identical, only one need be described in detail. With reference to pawl 14 and to FIG. 5, each of pawls 1316 has a flat end face 61 and a fiat side face 62 which intersect at an angle substantially equal to the angle at which the planes between adjacent side surfaces of adjacent major and minor teeth intersect, such angle being represented by angle A in FIG. 8. When the pawl is fully engaged with ratchet wheel 10, end face 61 lies flush with the adjacent side face of the major tooth engaged therewith and side face 62 lies flush with the side surface of the minor tooth engaged therewith and tangential to the apex of the next major tooth.

With reference to pawl 11 and FIG. 4, each driving pawl has a fiat end face 63 and a flat bottom face 65. When each driving pawl moves into engagement with ratchet wheel 10, end face 63 lies flush with the major tooth engaged therewith. When each driving pawl is fully actuated, bottom face 65 lies flush with the face of the minor tooth engaged therewith tangential to the apex of the succeeding major tooth. The angle between faces 63 and 65 is equal to the angle between adjacent side surfaces of a major and minor tooth less the angle through which the driving pawl pivots relative to the ratchet wheel as the ratchet wheel is stepped between succeeding adjacent positions, such angle being represented by angle B in FIG. 8.

Detent pawl 13 is arranged so that when fully engaged with ratchet wheel 10 a counterclockwise torque applied to ratchet wheel 10 tends to rotate pawl 13 in a clockwise direction toward the center of ratchet wheel 11 but, since ratchet wheel 10 is rigid, the detent pawl cannot move and therefore the actuating torgue is ineffective to rotate the ratchet wheel. Similarly, when stop pawl 15 fully engages ratchet wheel 10, the ratchet wheel cannot be rotated in a counterclockwise direction. Also, when either of detent pawl 14 or stop pawl 16 fully engages ratchet wheel 11 the ratchet wheel cannot be rotated in a clockwise direction. However, each of pawls 13, 14, 15 and 16 is ineffective to prevent rotation of the ratchet wheel in directions opposite to those described above since the teeth of the ratchet wheel could outwardly cam the pawl engaged therewith.

In operation, when neither of electromagnets 19 and 20 is energized, armatures 17 and 18 are in their unactuated positions wherein portions 4-4 and 48 engage a stop shim 64 secured to the upper surface of base 22. Spring 56 biases detent pawls 13 and 14 into full engagement with ratchet wheel 10 so that the ratchet wheel cannot be rotated in either direction. Spring 56, acting through the couplings between the detent pawls and their associated armatures, also biases armatures 17 and 18 against stop shim 64. Spring 55 biases stop pawl 15 so that edges 53 and 54 are engaged, the edges being so arranged that stop pawl 15 is disengaged from ratchet wheel 10. In a similar manner, spring 55 biases stop pawl 16 against detent pawl 13 so that the free end of stop pawl 16 is closely adjacent to but spaced from ratchet wheel 10.

When either of electromagnets 19 and 20 is energized, the parts move in a similar fashion except that end result is different. Actuation of electromagnet 19 causes ratchet wheel 10 to be rotated in a clockwise direction and actuation of electromagnet 20 causes rachet wheel 10 to be rotated in a counterclockwise direction. When electromagnet 20 is energized, it attracts armature 18 and rotates the armature from its unactuated position, shown in FIG. 1, toward its fully actuated position shown in FIG. 4. As armature 18 rotates or moves from its unactuated position and rotates counterclockwise, driving pawl 12 slides over guide 34 until it abuts the major tooth 57c aligned therewith, as shown in FIG. 2. However, before driving pawl 12 reaches this position, detent pawl 13 is disengaged from ratchet wheel 10, by arm 52, so that ratchet wheel It) can be rotated in a counterclockwise direction. Since detent pawl 13 is coupled to stop pawl 16, stop pawl 16 moves into engagement with ratchet wheel and, as viewed in FIGS. 2-4, lies immediately behind detent pawl 14.

As armature 18 rotates counterclockwise from the position shown in FIG. 2, it pushes major tooth 57c and rotates the ratchet wheel in a counterclockwise direction. Such rotation causes driving pawl 12 to be lifted from engagement with guide 34 toward engagement with stop 32, the driving pawl pivoting relative to the ratchet wheel generally at the intersection of the planes of the side surfaces of the major tooth and minor tooth engaged therewith.

As the ratchet wheel is rotated, major tooth 57d cams against the side surfaces 62 of detent pawl 14 and stop pawl 16 causing these pawls to be rotated in clockwise directions about pivot pin 35 until such time as major tooth 57d passes the tips of these pawls whereupon pawls 14 and 16 move, under the bias of springs 55 and 56, back into full engagement with the ratchet wheel. As detent pawl 14- is cammed in a clockwise direction, edges 50 and 51 separate the spring 55 moves stop pawl toward engagement with the ratchet wheel. The coupling between detent pawl 14 and stop pawl 15 is arranged so that major tooth 57c abut end face 61 of stop pawl 15 immediately prior to the time at which major tooth 57d passes by the tip of detent pawl 14. When stop pawl 15 engages tooth 57c as shown in FIG. 3, counterclockwise rotation of the ratchet wheel is stopped and further counterclockwise rotation of ratchet wheel 10 is prevented, the momentum of the ratchet wheel being ab sorbed by the stop pawl.

It should be noted that the direction of movement of major tooth 57a is nearly normal to the face of stop pawl 15 just before engagement therewith. Consequently, the tendency to wear of the coacting portions of the stop pawls and the ratchet wheel is minimized more effectively than in cases where the direction of movement is not so nearly normal.

When detent pawl 14 moves into full engagement with ratchet wheel 10 after major tooth 57d passes by, detent pawl 14 disengages stop pawl 15 by rotating it from engagement with the ratchet wheel 10 into the position illustrated in FIG. 4. When stop pawl 15 limits or stops the movement of ratchet wheel 10, the inertia of armature 18 and driving pawl 12 tends to cause the driving pawl 12 to slip over the apex of major tooth 570. However, stop 32 is arranged to prevent such movement, the stop being located so that when detent pawl 14 snaps back into engagement with the ratchet wheel, as shown in FIG. 4, driving pawl 12 lies fiush with stop 32.

When electromagnet is deenergized, detent pawl 13 and armature 18 are rotated clockwise by spring 56 into their unactuated positions. As driving pawl 12 moves from its fully actuated position toward its unactuated position, it slides over the apex of the next adjacent major tooth and then snaps back into engagement with guide 34, under the bias of the torsion springs 47, so that it is in position whereby subsequent energization of electromagnet 20 repeats the process or cycle just described.

Though only a single embodiment has been illustrated, it will be apparent to those skilled in the art that the invention here described can incorporate features of stepping motors of the type disclosed in the aforementioned application. Likewise, it will be apparent that many changes can be made in the details and arrangement of parts without departing from the scope of the invention defined in the appended claims.

What is claimed is:

1. A stepping motor comprising a ratchet wheel mounted for rotation about a first axis, said ratchet wheel having a plurality of evenly spaced major and minor teeth, each of said teeth being parallel to said first axis and having flat side surfaces and an apex, each of the side surfaces of each minor tooth lying in a plane which passes through the apex of the major tooth adjacent the other side surface of said minor tooth; a pivot pin spaced from said ratchet wheel and having an axis parallel to said first axis; first and second levers each rotatably mounted on said pivot pin and extending on opposite sides of said ratchet wheel; first and second electromagnets operatively mounted for rotating said first and second levers in response to energization of said first and second electromagnets respectively; first and second driving pawls each disposed on a different side of said ratchet wheel, said first and second driving pawls being carried by said first and second levers respectively, said first driving pawl being operative, upon actuation of said first lever, to rotate said ratchet wheel in a clockwise direction, said second driving pawl being operative, upon actuation of said second lever, to rotate said ratchet wheel in a counterclockwise direction; first and second detent pawls rotatably mounted on said pivot pin, each of said detent pawls being disposed on a different side of said ratchet wheel and being engageable therewith, said first detent pawl being operative when engaged with said ratchet wheel to prevent rotation of said ratchet wheel in a clockwise direction, said second detent pawl being operative when engaged with said ratchet wheel to prevent rotation of said ratchet wheel in a counterclockwise direction; means biasing said detent pawls toward engagernent with said ratchet wheel; means coupling said first lever and said first detent pawl and said second lever and said second detent pawl whereby actuation of each of said levers is eifective to disengage the detent pawl coupled therewith from said ratchet wheel to allow the ratchet wheel to be rotated; first and second stop pawls rotatably mounted on said pivot pin and engageable with said ratchet wheel to limit rotation thereof in clockwise and counterclockwise directions respectively, said biasing means being further operative to bias said stop pawls toward engagement with said ratchet wheel; and means coupling said first stop pawl and said first detent pawl and said second stop pawl and said second detent pawl whereby movement of each detent pawl in a direction away from engagement with said ratchet wheel allows said stop pawl coupled therewith to move toward engagement with said ratchet wheel under the bias of said biasing means.

2. A stepping motor in accordance with claim 1 including stop means engageable with said driving pawls to limit movement thereof.

3. In a stepping motor, the combination of a ratchet wheel having a peripheral series of evenly spaced teeth; means mounting said ratchet wheel for rotation about a fixed axis; first and second driving devices each com prising an electromagnet, a movable armature arranged for actuation by the electromagnet, and a driving pawl pivotally connected to the armature; means mounting said driving devices in such relation to each other and to said ratchet wheel that said driving pawls are spaced apart and a peripheral portion of said ratchet wheel is disposed therebetween, said armatures and driving pawls being so arranged that operation of the electromagnet of said first driving device causes the driving pawl of said first device to engage said ratchet wheel to rotate the same in a clockwise direction and operation of the electromagnet of said second driving device causes the driving pawl of said second device to engage said ratchet wheel to rotate the same in a counterclockwise direction; first and second movably mounted detent pawls spaced apart with a peripheral portion of said ratchet wheel disposed therebetween; first and second movably mounted stop pawls spaced apart with a peripheral portion of said ratchet wheel disposed therebetween, said first detent pawl and said first stop pawl each being movable into engagement with said ratchet wheel to prevent only clockwise rotation thereof, said second detent pawl and said second stop pawl each being movable into engagement with said ratchet wheel to prevent only counterclockwise rotation thereof; biasing means operatively arranged to bias said detent pawls and stop pawls toward said ratchet wheels, said detent pawls normally both engaging said ratchet wheel; movable abutment means normally engaging said stop pawls and effective, against action of said biasing means, to maintain said stop pawls disengaged from said ratchet wheel; means responsive to operation of the electromagnet of said first driving device and operatively connected to said first detent pawl to disengage the same from said ratchet wheel as the driving pawl of said first device is moved to rotate said wheel; means responsive to operation of the electromagnet of said second driving device and operatively connected to said second detent pawl to disengage the same from said ratchet wheel as the driving pawl of said second device is moved to rotate said wheel; and means whereby said abutment means is shifted to allow said first stop pawl to move into engagement with said ratchet wheel after said first detent pawl is disengaged therefrom and said second stop pawl to move into engagement with said ratchet wheel after said second detent pawl is disengaged therefrom.

4-. A stepping motor in accordance with claim 3 and including stop means mounted in the path of movement of said driving pawls and operative to limit movement of said driving pawls.

5. A stepping motor in accordance with claim 3 and wherein said armatures, said detent pawls and said stop pawls are all mounted for pivotal movement about a common axis parallel to the axis of rotation of said ratchet wheel.

6. In a bidirectional stepping motor, the combination of a ratchet wheel having a peripheral series of evenly spaced teeth; means mounting said ratchet wheel for rotation about a fixed axis; a pair of driving pawls spaced from each other with a peripheral port-ion of said ratchet wheel disposed therebetween, said driving pawls each being mounted for movement toward and away from said ratchet wheel; electromagnetic power means operatively arranged for selectively actuating said driving pawls, actuation of one of said driving pawls causing clockwise rotation of said ratchet wheel and actuation of the other of said driving pawls causing counterclockwise rotation of said ratchet wheel; first and second movable mounted detent pawls spaced apart with a peripheral portion of said ratchet wheel disposed therebetween; first and second movably mounted stop pawls spaced apart with a peripheral portion of said ratchet wheel disposed therebetween, said first detent pawl and said first stop pawl being engageable with said ratchet wheel to prevent clockwise rotation thereof, said second detent pawl and said second stop pawl being engageable with said ratchet wheel to prevent counterclockwise rotation thereof; resilient means biasing said detent pawls and stop pawls toward engagement with said ratchet wheels, said resilient means being effective to maintain both of said detent pawls normally engaged with said ratchet wheel; abutment means carried by said first detent pawl and engaged by said second stop pawl to maintain the latter disengaged from said ratchet wheel so long as said first detent pawl is engaged with said ratchet wheel; abutment means carried by said second detent pawl and engaged by said first stop pawl to maintain the latter disengaged from said ratchet wheel so long as said second detent pawl is engaged with said ratchet wheel; means whereby actuation of said one driving pawl toward said ratchet wheel moves said first detent pawl out of engagement with said ratchet wheel; and means whereby actuation of said other driving pawl toward said ratchet wheel moves said second detent pawl out of engagement with said ratchet wheel, said detent pawls, when engaged with said ratchet Wheel, being successively oammed against the biasing action of said resilient means by the teeth of said ratchet wheel, as the wheel is rotated, and each such camming action serving to shift the corresponding one of said abutment means to allow the corresponding stop pawl to engage said ratchet wheel.

7. A stepping motor in accordance with claim 6 and wherein said detent pawls and stop pawls are mounted for pivotal movement about a common axis parallel to the axis of rotation of said ratchet wheel.

8. A stepping motor in accordance with claim 7 and wherein said electromagnetic power means comprises two armatures, each of said driving pawls being pivotally connected to a diiferent one of said armatures, said armatures being mounted for pivotal movement about said common ElXlS.

9. A stepping motor in accordance with claim 6 and wherein said resilient means comprises a first spring connected between said detent pawls and a second spring connected between said stop pawls.

10. In a bidirectional stepping motor, the combination of a ratchet wheel having a peripheral series of evenly spaced teeth; means mounting said ratchet wheel for rotation about a fixed axis; a pair of movable driving pawls spaced from each other with a peripheral portion of said ratchet wheel disposed therebetween; electromagnetic power means operatively arranged for selectively operating said driving pawls, actuation of one of said driving pawls causing clockwise rotation of said ratchet wheel and actuation of the other of said driving pawls causing counterclockwise rotation of said ratchet wheel; first and second movably mounted detent pawls spaced apart with a peripheral portion of said ratchet wheel disposed therebetween; first and second movably mounted stop pawls spaced apart with a peripheral portion of said ratchet wheel disposed therebetween, said first detent pawl and said first stop pawl each being engageable with said ratchet wheel to prevent clockwise rotation thereof, said second detent pawl and said second stop pawl each being engageable with said ratchet wheel to prevent countercloclc wise rotation thereof, said detent pawls both being resiliently biased into normal engagement with said ratchet wheel when neither of said driving pawls is actuated by said power means, said stop pawls being resiliently biased toward said ratchet wheel; means whereby said first detent pawl 18 positively disengaged from said ratchet wheel upon actuation of said one driving pawl to drive said ratchet wheel; means whereby said second detent pawl is positively disengaged from said ratchet wheel upon actuation of said other driving pawl to drive said ratchet wheel; and movable abutment means normally engaging said stop pawls and maintaining the same disengaged from said ratchet wheel, said abutment means being operated to release said first stop pawl for engagement with said ratchet wheel only upon passage of a tooth of said ratchet wheel by said second detent pawl while the latter is engaged with said ratchet Wheel and to release said second stop pawl for engagement with said ratchet wheel only upon passage of a tooth of said ratchet wheel by said first detent pawl while the latter is engaged with said ratchet wheel.

11. In a bidirectional stepping motor, the combination of a toothed ratchet wheel mounted for rotation about a fixed axis; first and second movably mounted driving pawls spaced apart with a portion of said ratchet wheel disposed therebetween; power means for selectively actuating said driving pawls, actuating of said first driving pawl causing clockwise rotation of said ratchet Wheel, actuation of said second driving pawl causing counterclockwise rotation of said ratchet wheel; first and second movably mounted detent pawls spaced apart with a peripheral portion of said ratchet wheel disposed therebetween; first and second movably mounted stop pawls spaced apart with a peripheral portion of said ratchet wheel disposed therebetween, said first detent pawl and said first stop pawl being engageable with said ratchet wheel to prevent clockwise rotation thereof, said second detent pawl and said second stop pawl being engageable with said ratchet wheel to prevent counterclockwise rotation thereof, said detent pawls both being normally biased into engagement with said ratchet wheel; means responsive to operation of said power means and operatively connected to said detent pawls to positively disengage the same selectively from said ratchet wheel in accordance with the direction of rotation of said ratchet wheel to be accomplished; and means for selectively moving said stop pawls into engagement with said ratchet wheel in response to movement of individual teeth of said ratchet wheel relative to the one of said detent pawls engaged with the ratchet wheels.

12. In a bidirectional stepping motor, the combination of a toothed ratchet wheel mounted for rotation about a fixed axis; first and second movably mounted driving pawls spaced apart with a portion of said ratchet wheel therebetween; power means for selectively actuating said pawls, actuation of said first driving pawl causing clockwise rotation of said ratchet wheel and actuation of said second driving pawl causing counterclockwise rotation of said ratchet wheel; first and second movably mounted detent pawls spaced apart with a portion of said ratchet wheel therebetween; first and second movably mounted stop pawls spaced apart with a portion of said ratchet wheel therebetween, said first detent pawl and first stop pawl being engageable with said ratchet wheel to prevent clockwise rotation thereof, said second detent pawl and second stop pawl being engageable with said ratchet wheel to prevent counterclockwise rotation thereof; resilient means operatively connected to said detent pawls and stop pawls, said resilient means being efiective to bias both of said detent pawls into normal engagement with said ratchet wheel and to bias said stop pawls both toward engagement with said ratchet wheel; movable abutment means operatively disposed to hold said stop pawls normally out of engagement with said ratchet wheel; means responsive to operation of said power means and operatively associated with said detent pawls to positively disengage the same selectively from said ratchet wheel in accordance with the direction of rotation of said ratchet wheel to be accomplished by such operation of the power means, said first detent pawl riding yieldably over the teeth of said ratchet wheel when said ratchet wheel is rotated counterclockwise and being successively cammed 10 away from said ratchet wheel during such rotation by the successive passage of ratchet wheel teeth, said second detent pawl riding yieldably over the teeth of said ratchet wheel during clockwise rotation thereof and being similarly cammed away from said ratchet wheel by the successive passage of ratchet wheel teeth; and means operative to move said abutment means to allow said first stop pawl to engage said ratchet wheel only in response to such camming of said second detent pawl and to allow said second stop pawl to engage said ratchet wheel only in response to such camming of said first detent pawl.

13. In a bidirectional stepping device, the combination of a toothed ratchet wheel mounted for rotation about a fixed axis; first and second movable driving pawls spaced apart with a portion of said ratchet wheel therebetween; power means for selectively actuating said driving pawls, actuation of said first driving pawl causing said ratchet wheel to rotate in a clockwise direction and actuation of said second driving pawl causing said ratchet wheel to rotate in a counterclockwise direction; first and second movably mounted detent pawls spaced apart with a portion of said ratchet wheel therebetween; first and second movably mounted stop pawls spaced apart with a portion of said ratchet wheel therebetween, said first detent pawl and first stop pawl each being engageable with said ratchet wheel to prevent clockwise rotation thereof, said second detent pawl and second stop pawl each being engageable with said ratchet wheel to prevent counterclockwise rotation thereof; resilient means operatively connected to said detent pawls to bias both of the same into normal engagement with said ratchet wheel, said stop pawls both being normally disengaged from said ratchet wheel; means responsive to operation of said power means and operatively associated with said detent pawls to disengage the same selectively from said ratchet wheel in accordance with the direction of rotation of said ratchet wheel to be accomplished by such operation of said power means; and means responsive to occurrence of a predetermined amount of rotary movement of said ratchet wheel for selectively engaging said stop pawls with said ratchet wheel to positively stop such movement.

References Cited in the file of this patent UNITED STATES PATENTS 321,523 Palmer July 7, 1885 2,406,220 Hines Aug. 20, 1946 FOREIGN PATENTS 1,120,691 France Apr. 23, 1956 

1. A STEPPING MOTOR COMPRISING A RATCHET WHEEL MOUNTED FOR ROTATION ABOUT A FIRST AXIS, SAID RATCHET WHEEL HAVING A PLURALITY OF EVENLY SPACED MAJOR AND MINOR TEETH, EACH OF SAID TEETH BEING PARALLEL TO SAID FIRST AXIS AND HAVING FLAT SIDE SURFACES AND AN APEX, EACH OF THE SIDE SURFACES OF EACH MINOR TOOTH LYING IN A PLANE WHICH PASSES THROUGH THE APEX OF THE MAJOR TOOTH ADJACENT THE OTHER SIDE SURFACE OF SAID MINOR TOOTH; A PIVOT PIN SPACED FROM SAID RATCHET WHEEL AND HAVING AN AXIS PARALLEL TO SAID FIRST AXIS; FIRST AND SECOND LEVERS EACH ROTATABLY MOUNTED ON SAID PIVOT PIN AND EXTENDING ON OPPOSITE SIDES OF SAID RATCHET WHEEL; FIRST AND SECOND ELECTROMAGNETS OPERATIVELY MOUNTED FOR ROTATING SAID FIRST AND SECOND LEVERS IN RESPONSE TO ENERGIZATION OF SAID FIRST AND SECOND ELECTROMAGNETS RESPECTIVELY; FIRST AND SECOND DRIVING PAWLS EACH DISPOSED ON A DIFFERENT SIDE OF SAID RATCHET WHEEL, SAID FIRST AND SECOND DRIVING PAWLS BEING CARRIED BY SAID FIRST AND SECOND LEVERS RESPECTIVELY, SAID FIRST DRIVING PAWL BEING OPERATIVE, UPON ACTUATION OF SAID FIRST LEVER, TO ROTATE SAID RATCHET WHEEL IN A CLOCKWISE DIRECTION, SAID SECOND DRIVING PAWL BEING OPERATIVE, UPON ACTUATION OF SAID SECOND LEVER, TO ROTATE SAID RATCHET WHEEL IN A COUNTERCLOCKWISE DIRECTION; FIRST AND SECOND DETENT PAWLS ROTATABLY MOUNTED ON SAID PIVOT PIN, EACH OF SAID DETENT PAWLS BEING DISPOSED ON A DIFFERENT SIDE OF SAID RATCHET WHEEL AND BEING ENGAGEABLE THEREWITH, SAID FIRST DETENT PAWL BEING OPERATIVE WHEN ENGAGED WITH SAID RATCHET WHEEL TO PREVENT ROTATION OF SAID RATCHET WHEEL IN A CLOCKWISE DIRECTION, SAID SECOND DETENT PAWL BEING OPERATIVE WHEN ENGAGED WITH SAID RATCHET WHEEL TO PREVENT ROTATION OF SAID RATCHET WHEEL IN A COUNTERCLOCKWISE DIRECTION; MEANS BIASING SAID DETENT PAWLS TOWARD ENGAGEMENT WITH SAID RATCHET WHEEL; MEANS COUPLING SAID FIRST LEVER AND SAID FIRST DETENT PAWL AND SAID SECOND LEVER AND SAID SECOND DETENT PAWL WHEREBY ACTUATION OF EACH OF SAID LEVERS IS EFFECTIVE TO DISENGAGE THE DETENT PAWL COUPLED THEREWITH FROM SAID RATCHET WHEEL TO ALLOW THE RATCHET WHEEL TO BE ROTATED; FIRST AND SECOND STOP PAWLS ROTATABLY MOUNTED ON SAID PIVOT PIN AND ENGAGEABLE WITH SAID RATCHET WHEEL TO LIMIT ROTATION THEREOF IN CLOCKWISE AND COUNTERCLOCKWISE DIRECTIONS RESPECTIVELY, SAID BIASING MEANS BEING FURTHER OPERATIVE TO BIAS SAID STOP PAWLS TOWARD ENGAGEMENT WITH SAID RATCHET WHEEL; AND MEANS COUPLING SAID FIRST STOP PAWL AND SAID FIRST DETENT PAWL AND SAID SECOND STOP PAWL AND SAID SECOND DETENT PAWL WHEREBY MOVEMENT OF EACH DETENT PAWL IN A DIRECTION AWAY FROM ENGAGEMENT WITH SAID RATCHET WHEEL ALLOWS SAID STOP PAWL COUPLED THEREWITH TO MOVE TOWARD ENGAGEMENT WITH SAID RATCHET WHEEL UNDER THE BIAS OF SAID BIASING MEANS. 